A collection of pornographic magazines, typically located in the bathroom or bedroom that is used to visually aid the jacking off or masturbation process. This collection of magazines usually includes periodicals such as; Jugs, Beaver, Ass Jacks, Hustler, etc.
Wayne: Dude, you see the Jack Stack in Bruce's bathroom? Wow, impressive!
Frank: Yeah man, that was killer! I had to open them up and rub one off when I was at his house last week!